From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9471EC433E9 for ; Thu, 3 Sep 2020 17:43:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 768CE20775 for ; Thu, 3 Sep 2020 17:43:55 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="lDIe7CF5" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728468AbgICRnw (ORCPT ); Thu, 3 Sep 2020 13:43:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37970 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726025AbgICRnv (ORCPT ); Thu, 3 Sep 2020 13:43:51 -0400 Received: from mail-il1-x143.google.com (mail-il1-x143.google.com [IPv6:2607:f8b0:4864:20::143]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 14337C061244; Thu, 3 Sep 2020 10:43:50 -0700 (PDT) Received: by mail-il1-x143.google.com with SMTP id t16so3559401ilf.13; Thu, 03 Sep 2020 10:43:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=vYFQYSTb/+17+Uuu6516MdUuM986Y6u14DKyOKGcWYc=; b=lDIe7CF5KDUMWGocKm7G/UyV8gRmhYQGDRCGTIRYgdBTWVP2fg0DSI64zyl1Yz3HkQ zZWprpbGlgiLAhJ0Cj/FVEMcDQDo/2a/18ft6tpgWCivMWuEFKVIqqsQm45BWgLsVAAg VO+5qHy5uw0D4m8fLee46jmvFtq4FsPhV3wicZevOT+Fylc1KSGW2ZbYn3KqWl4kQq+3 9zj4maCKAJ1vxn1TTIM7yKmFX9ofN+p7Rzhxc6EzLUkZLn7v7q2V5eVpCZjtggAOw8q2 ZJ+irFc04GnA1cr4U17yqm8gbatsuwQwuJ0F9KGkn+WPyT9+ZfB4OwLNPIFn5V1d+nXG TKaA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=vYFQYSTb/+17+Uuu6516MdUuM986Y6u14DKyOKGcWYc=; b=p4zqLcCpNrTQ8Qv8JtieTmdGvgOHxe5o8RIkhyF2yyu1tVLN4VflDpnpd8cqmurb/z LEu435feT4dci3RlIH+YtniFmhthwS5ryLMBe5Uglqez+nvPg69CIx7ZWNOO9jVLxg1D BIMdnJVp81SDd1znP2ZaMp6sYn8HBMOJyf8EvfQqCxrLnluabI9Iz5efepUR6sIlTQPi VYqwNkHxJK7ZSsWeIvkYtH5RKaShGF0CzzRyHMpLnQHcaBfz6T1xAenvRmg2DdVppGHG g4yimHJsZ/IqOt9PBYlAnEk9syZMJiMD6EC0l8iVEHKy2saH+PSrEtMAKItV93Uxfr7Y urOw== X-Gm-Message-State: AOAM530FWGaTzbpPl+zpbpOUjPlMdHixnb/oHeGodeAc3LOrctMeD7Uc JIJARrHUmMb1AFftTOCVV1oVIwcmxpnNqhceyw4= X-Google-Smtp-Source: ABdhPJx0zkJhJo3i54QacP+Oa+oDBL1udk+DNdAoRc0FIBWni3OthGQzgu/4UVLEGNHGQu1+46yOMMXqiGNlx9lWZKk= X-Received: by 2002:a92:9145:: with SMTP id t66mr4170348ild.305.1599155030104; Thu, 03 Sep 2020 10:43:50 -0700 (PDT) MIME-Version: 1.0 References: <465a540e-5296-32e7-f6a6-79942dfe2618@netrounds.com> <20200623134259.8197-1-mzhivich@akamai.com> <1849b74f-163c-8cfa-baa5-f653159fefd4@akamai.com> <7fd86d97-6785-0b5f-1e95-92bc1da9df35@netrounds.com> <500b4843cb7c425ea5449fe199095edd5f7feb0c.camel@redhat.com> <25ca46e4-a8c1-1c88-d6a9-603289ff44c3@akamai.com> <20200822032800.16296-1-hdanton@sina.com> <20200825032312.11776-1-hdanton@sina.com> <20200825162329.11292-1-hdanton@sina.com> <5f46032e.1c69fb81.9880c.7a6cSMTPIN_ADDED_MISSING@mx.google.com> <20200827125747.5816-1-hdanton@sina.com> In-Reply-To: From: Cong Wang Date: Thu, 3 Sep 2020 10:43:38 -0700 Message-ID: Subject: Re: Packet gets stuck in NOLOCK pfifo_fast qdisc To: Paolo Abeni Cc: Kehuan Feng , Hillf Danton , Jike Song , Josh Hunt , Jonas Bonn , Michael Zhivich , David Miller , John Fastabend , LKML , Netdev Content-Type: text/plain; charset="UTF-8" Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Thu, Sep 3, 2020 at 1:40 AM Paolo Abeni wrote: > > On Wed, 2020-09-02 at 22:01 -0700, Cong Wang wrote: > > Can you test the attached one-line fix? I think we are overthinking, > > probably all > > we need here is a busy wait. > > I think that will solve, but I also think that will kill NOLOCK > performances due to really increased contention. Yeah, we somehow end up with more locks (seqlock, skb array lock) for lockless qdisc. What an irony... ;) > > At this point I fear we could consider reverting the NOLOCK stuff. > I personally would hate doing so, but it looks like NOLOCK benefits are > outweighed by its issues. I agree, NOLOCK brings more pains than gains. There are many race conditions hidden in generic qdisc layer, another one is enqueue vs. reset which is being discussed in another thread. Thanks.